During the first two years of the project, over 30 new steroid derivatives have been synthesized and labeled as fluorescent agents. During the second year of the study, careful correlation with estrogen receptor status in 20 patients was obtained with good results (P less than .01). Great variability in labeling was observed due to impurities in the fluorescent derivatives, and for this reason, extensive investigation was carried out to improve synthetic methods, and rigidly establish structures. At present, the synthesis of any fluorescent labelled derivative of the steroid is possible by several pathways, and within the last month it has been possible to purify these compounds completely free of their parent steroid by recrystallization techniques. All the radiographic methods have been developed for correlation with the steroid receptor uptake, and tritium labelled compounds will be submitted to collaborators for verification of biologic activity (and absence of hydrolysis) of the new synthetic compounds. A correlative study of human endometrium as a model for receptor utilizing fluorescent steroid autoradiography and thymidine proliferative index is under way to evaluate the behavior of these compounds in normal target tissue. During the third year, correlation of behavior of the fluorescent steroids in autoradiography of the estradiol and related steroids will be carried out, as well as correlation of its behavior within animals, and their natural target tissues. Further clinical work, evaluating the utility of fluorescent steroid uptake and cancer therapeutic response is planned.